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Abstract— The dose dependence of chromosomal aberration frequencies induced by UV light in G1Xenopus cells has been examined. Total aberration frequencies did not exceed control levels until a dose of approximately 7.5 Jm-2 was administered. Chromatid type aberrations were prevalent throughout the dose range 7.5–25.0 Jm-2. Chromosome type aberration frequencies were comparatively low but exceeded control levels throughout the range 10.0–25.0 Jm-2, Results of supporting experiments suggested that most of the chromosome type aberrations observed were in the second mitosis following exposures and were derived from aberrations which normally appear as chromatid types at the first mitosis following exposures. 相似文献
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Existing theories which deal with the isotope dependence of vibronic structure have neglected the isotope dependence of vibration dynamics. The latter dependence (isotope dynamic mixing) is an adiabatic correction to vibronic structure theory. A theory of vibronic structure, which includes isotope dynamic mixing, is developed. The results of model calculations are presented. 相似文献
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Owens TM Ludwig BJ Fosnacht DR Bartolin JM Homann N Wells NJ Orr BG Banaszak Holl MM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(26):11422-11427
Chemisorbed monolayers of octylgermane (C8H17GeH3) on gold have been formed by vapor deposition in ultrahigh vacuum. The monolayer has been characterized by X-ray photoelectron and reflection absorption infrared spectroscopies (XPS and RAIRS) and scanning tunneling microscopy (STM). XPS data indicate the monolayer can be oxidized by exposure to ozone. STM images exhibit a complex pattern which can be modeled as strain-mediated spinodal decomposition. 相似文献
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Mecke A Majoros IJ Patri AK Baker JR Holl MM Orr BG 《Langmuir : the ACS journal of surfaces and colloids》2005,21(23):10348-10354
Polycationic polymers are used extensively in biology to disrupt cell membranes and thus enhance the transport of materials into the cell. The highly polydisperse nature of many of these materials makes obtaining a mechanistic understanding of the disruption processes difficult. To design an effective mechanistic study, a monodisperse class of polycationic polymers, poly(amidoamine) (PAMAM) dendrimers, has been studied in the context of supported dimyristoylphosphatidylcholine (DMPC) lipid bilayers using atomic force microscopy (AFM). Aqueous solutions of amine-terminated generation 7 (G7) PAMAM dendrimers caused the formation of 15-40-nm-diameter holes in lipid bilayers. This effect was significantly reduced for smaller G5 dendrimers. For G3, no hole formation was observed. In addition to dendrimer size, surface chemistry had a strong influence on dendrimer-lipid bilayer interactions. In particular, acetamide-terminated G5 did not cause hole formation in bilayers. In all instances, the edges of bilayer defects proved to be points of highest dendrimer activity. A proposed mechanism for the removal of lipids by dendrimers involves the formation of dendrimer-filled lipid vesicles. By considering the thermodynamics, interaction free energy, and geometry of these self-assembled vesicles, a model that explains the influence of polymer particle size and surface chemistry on the interactions with lipid membranes was developed. These results are of general significance for understanding the physical and chemical properties of polycationic polymer interactions with membranes that lead to the transport of materials across cell membranes. 相似文献